diff --git a/src/libgit2/indexer.c b/src/libgit2/indexer.c
index f1c7e437c61..6b726a694b8 100644
--- a/src/libgit2/indexer.c
+++ b/src/libgit2/indexer.c
@@ -97,7 +97,7 @@ static int parse_header(struct git_pack_header *hdr, struct git_pack_file *pack)
 	int error;
 	git_map map;
 
-	if ((error = p_mmap(&map, sizeof(*hdr), GIT_PROT_READ, GIT_MAP_SHARED, pack->mwf.fd, 0)) < 0)
+	if ((error = p_mmap(&map, sizeof(*hdr), GIT_PROT_READ, GIT_MAP_PRIVATE, pack->mwf.fd, 0)) < 0)
 		return error;
 
 	memcpy(hdr, map.data, sizeof(*hdr));
diff --git a/src/util/futils.c b/src/util/futils.c
index 25c3a1be180..00877f4d933 100644
--- a/src/util/futils.c
+++ b/src/util/futils.c
@@ -359,7 +359,7 @@ int git_futils_mv_withpath(const char *from, const char *to, const mode_t dirmod
 
 int git_futils_mmap_ro(git_map *out, git_file fd, off64_t begin, size_t len)
 {
-	return p_mmap(out, len, GIT_PROT_READ, GIT_MAP_SHARED, fd, begin);
+	return p_mmap(out, len, GIT_PROT_READ, GIT_MAP_PRIVATE, fd, begin);
 }
 
 int git_futils_mmap_ro_file(git_map *out, const char *path)
diff --git a/tests/util/futils.c b/tests/util/futils.c
index 993b14d9b03..f15d066c24f 100644
--- a/tests/util/futils.c
+++ b/tests/util/futils.c
@@ -1,6 +1,10 @@
 #include "clar_libgit2.h"
 #include "futils.h"
 
+#if !defined(GIT_WIN32) && !defined(NO_MMAP)
+#include <sys/mman.h>
+#endif
+
 /* Fixture setup and teardown */
 void test_futils__initialize(void)
 {
@@ -37,6 +41,30 @@ void test_futils__writebuffer(void)
 	git_str_dispose(&append);
 }
 
+void test_futils__mmap_ro_uses_map_private(void)
+{
+#if defined(GIT_WIN32) || defined(NO_MMAP)
+	cl_skip();
+#else
+	const char content[] = "mapped data";
+	const char *path = "futils/mmap-file";
+	git_map map = { 0 };
+	git_file fd;
+
+	cl_git_mkfile(path, content);
+	cl_assert((fd = p_open(path, O_RDWR)) >= 0);
+	cl_git_pass(git_futils_mmap_ro(&map, fd, 0, sizeof(content) - 1));
+
+	/* A private mapping must not propagate changes back to the file. */
+	cl_must_pass(mprotect(map.data, map.len, PROT_READ | PROT_WRITE));
+	((char *)map.data)[0] = 'M';
+	cl_assert_equal_file(content, sizeof(content) - 1, path);
+
+	git_futils_mmap_free(&map);
+	p_close(fd);
+#endif
+}
+
 void test_futils__write_hidden_file(void)
 {
 #ifndef GIT_WIN32